The present invention relates to systems for controlling transmission lines in a redundant system and interface units therefor, and more particularly to a system for controlling transmission lines connected to a transmission apparatus having a redundant configuration such as a multiplex transmission apparatus.
In transmission apparatuses such as a multiplex transmission apparatus or a cross connect apparatus having an optical interface, the quality of transmitting information is secured by means of a redundant transmission system.
In the transmission apparatus employing the redundant configuration which includes transmission lines forming a working (or main) system and a protection (or sub) system, there is a demand to reduce the power consumption of the transmission apparatus as a whole by reducing the power consumption of the unused protection system in an optical interface board.
FIG. 1 shows an example of redundant configuration of a transmission system which comprises transmission apparatuses 11 and 12 connected via optical transmission lines 13 and 14. The transmission apparatus 11 includes optical interface boards 15 and 17 which are respectively connected to optical interface boards 16 and 18 of the transmission apparatus 12 via the optical transmission lines 13 and 14. As may be seen from FIG. 1, selectors 19 and 20 are operated so that the corresponding pair consisting of the optical interface boards 15 and 16 are used as the working system and the pair consisting of the optical interface boards 17 and 18 are used as the protection system, or vice versa.
FIG. 2 shows the construction of an example of a conventional optical interface board which receives an optical signal having a transmission speed of 150 Mbit/s or 50 Mbit/s from a transmission line. The optical interface board includes: an opto-electric (O/E) converter 21 for converting an optical signal into an electrical signal, an electro-optic (E/O) converter 22 for converting an electrical signal into an optical signal, a transmission line signal processor 23 for processing transmission line signals which are exchanged, and an apparatus interface 24 for providing an interface between the transmission line signal processor 23 and a transmission apparatus (not shown). The illustration of a power supply and a clock generator is omitted in FIG. 2.
In the transmission line signal processor 23, a received signal from the O/E converter 21 is subjected to a frame synchronization detection of the input signal in a frame synchronization unit 25, subjected to an error detection of the input signal in a transmission line error detector 26, subjected to an overhead detection of the input signal in an overhead detection unit 27, and is subjected to a pointer detection of the input signal in a pointer detection unit 28. Thereafter, the signal from the transmission signal line processor 23 is supplied to the transmission apparatus via the apparatus interface 24.
A transmitting signal from the transmission apparatus is input to the transmission line signal processor 23 via the apparatus interface 24. The pointer adding unit 29 adds a pointer to the output signal, and an overhead adding unit 30 adds an overhead to the output signal. A transmission line error detection signal is added into the output signal in a transmission line error detection signal adding unit 31. The E/O converter 22 then converts the output signal into an optical signal which is supplied to the transmission line.
Referring to FIG. 1, the optical interface boards in the working system and the protection system are both supplied with power at all times. This means that when there are equal numbers of working optical interface boards and protection optical interface boards, the power consumed by the protection optical interface boards amounts to half the total power consumption of all the optical interface boards.
Thus, a problem with the conventional transmission apparatus is that the protection optical interface boards are supplied with power at all times, and that they are always activated for transmission line signal processing in the same manner as their counterparts in the working system. The reduction in the power consumption in a protection interface board is possible if the processing within the protection optical interface board can be reduced compared to that of the working optical interface board. This then would result in the reduction of power consumption of the transmission apparatus as a whole. Conventionally, however, no such proposal has been made.